Does hydrostatic pressure influence lumpfish (Cyclopterus lumpus) heart rate and its response to environmental challenges?

Abstract

Studies on the effects of environmental changes with increasing depth (e.g. temperature and oxygen level) on fish physiology rarely consider how hydrostatic pressure might influence the observed responses. In this study, lumpfish (Cyclopterus lumpus, 200–400 g), which can exhibit vertical migrations of over 100 m daily and can be found at depths of 500 m or more, were implanted with Star-Oddi micro-HRT loggers. Then, their heart rate (fH) was measured in a pressure chamber when exposed to the following: (i) increasing pressure (up to 80 bar; 800 m in depth) at 10°C or (ii) increasing temperature (12–20°C), decreasing temperature (12 to 4°C) or decreasing oxygen levels (101–55% air saturation at 12°C) in the absence or presence of 80 bar of pressure. Additionally, we determined their fH response to chasing and to increasing temperature (to 22°C) at atmospheric pressure. Pressure-induced increases in fH (e.g. from 48 to 61 bpm at 12°C) were associated with hyperactivity. The magnitude of the rise in fH with temperature was greater in pressure-exposed vs. control fish (i.e. by ~30 bpm vs. 45 bpm between 5°C and 20°C). However, the relative increase (i.e. slope of the relationship) was not different between groups. In contrast, 80 bar of pressure eliminated the small (5 bpm) increase in fH when control fish were exposed to hypoxia. Exhaustive exercise and increasing temperature to 22°C resulted in a maximum fH of 77 and 81 bpm, respectively. Our research shows that pressure influences the fH response to environmental challenges and provides the first evidence that lumpfish have a limited capacity to increase fH.

Atlantic Salmon (Salmo salar) Cage-Site Distribution, Behavior, and Physiology During a Newfoundland Heat Wave

“…However, this was unlikely to have been the cause of the salmon mortalities in this study as the surgeon (Z.A.Z.) had considerable experience (see Zrini and Gamperl, 2021 ; Zrini et al, 2021 ) and surgical times were short (average 12 min). That said, recovery location might have been a contributing factor.…”

The behavior and welfare of neglected species: some examples from fish and mammals

“…These animals are cold blooded and thus the environmental temperature has a substantial impact on their physiology. Heart rate measurements in response to increased temperature and exercise demonstrated that lumpfish have a relatively poor response with a low maximal heart rate and thus these fish are unlikely to perform well under conditions when temperatures rise ( Zrini, Sandrelli & Gamperl, 2021 ). Preference studies show adult lumpfish prefer 6–7 °C but on land production of these animals is typically 10 °C ( Mortensen et al, 2020 ).…”

Regulation of heart rate in vertebrates during hypoxia: A comparative overview

“…Winter flounder ( Pseudopleuronectes americanus ) exhibits hypoxic bradycardia at 8 but not 15°C 133 . It was recently shown in lumpfish ( Cyclopterus lumpus ) that mild hypoxia results in a small increase in heart rate, although this was prevented by elevated hydrostatic pressure simulating increased water depth 134 . In carp ( Cyprinus carpio ), moderate hypoxia is met with an initial tachycardia which then declines, but only to resting levels 13 .…”

“…133 It was recently shown in lumpfish (Cyclopterus lumpus) that mild hypoxia results in a small increase in heart rate, although this was prevented by elevated hydrostatic pressure simulating increased water depth. 134 In carp (Cyprinus carpio), moderate hypoxia is met with an initial tachycardia which then declines, but only to resting levels. 13 In rainbow trout (Oncorhynchus mykiss), perhaps the most well studied of all teleost fishes in comparative physiology (at least before the emergence of zebrafish as a model organism), both classic [135][136][137] and more recent 138 studies have described the archetypal piscine hypoxic bradycardia.…”